Method and Apparatus for Reducing Organic Waste by Rotary Desiccation

ABSTRACT

A machine is described that reduces landfill and compost waste streams by processing the waste at the site of generation. The process used, rotary desiccation, is fast, energy efficient, generates no greenhouse gasses and the end product is both sterile and suitable for immediate use as a pellet fuel or other biomass uses. 
     The machine integrates a number of sub-components (grinder, de-waterer, desiccation drum, separation devices) in new and non-obvious ways that automatically process and sort organic wastes and contaminants with no intervention from operators and very little maintenance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Application No. 61/601,881, filed on 2012, Feb. 22, with the title “Apparatus for Reducing Organic Waste by Rotary Desiccation”

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This section is not applicable

SEQUENCE LISTING/COMPUTER PROGRAM LISTING

This section is not applicable

BACKGROUND OF INVENTION

There is a continuing shortage of landfill space in the US, but it's not because of a lack of raw acreage. A recent study shows that, at current waste production rates, all of the non-hazardous waste from the entire US for the next millennium could be stored in a site 35 miles on a side and 300 feet deep. The problem is that landfills are politically unpopular and it is becoming increasingly difficult to find acceptable locations for new ones. Additionally, older landfills, or ones that are poorly operated, can cause environmental damage due to leachate contamination of groundwater and emissions of methane and CO₂ into the atmosphere.

The most expedient way of dealing with a landfill shortage is to extend the life of existing landfills by reducing the volume of material going into them. A good initial step was the creation of large-scale windrow composting centers starting in the 1990′s. These reduce the waste streams into landfills by diverting organic waste (plant material, animal material and food-contaminated paper products) to composting centers where they are processed in the traditional manner by aerobic bacterial decomposition.

However, compost centers have many of the same objections posed by the public as landfills, namely the inconvenience and noise of continuous large truck traffic and the offensive odors generated during composting. Since this process takes weeks or months to complete, any center serving a large city or county requires a large parcel of land for its operation. Additionally, the collection process itself, which uses large trucks, has the attendant problems of being petroleum intensive while producing air pollutants and greenhouse gasses.

A more efficient approach is to process organic waste on-site by means of dehydration. The Invention described uses a process of complete desiccation with temperatures and durations extreme enough to both physically breakdown the materials and kill all bacteria. The end result produces a biomass material that has market value.

BRIEF SUMMARY OF INVENTION

The Invention is an in-vessel processor that reduces the weight and volume of organic waste by up to 95%. It is a continuous-feed rotary desiccator with an isolating feed hopper that allows organic waste material to be added at any time without stopping the unit. Material that has finished processing is removed by a density separator into a storage bin while material still being processed remains in the machine. High density contaminants, such as glass, metal and bone fragments remain in the machine until the end of the process run and then are automatically removed for recycling or disposal.

The finished product is sterile with all organisms and seeds killed by the process heat. The product has several potential uses as a pellet fuel, soil amendment or animal feed, any of which reduces the landfill stream by 100%.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 External View

FIG. 2 Process Flow

FIG. 3 Mechanism Arrangement

-   -   FIG. 3A Left Quarter View     -   FIG. 3B Right Quarter View

It is suggested that FIG. 3 be used as the Front Page View. This figure has two sub-views. If only one view must be chosen, it is suggested that FIG. 3B (Right Quarter View) be used.

FIG. 4 Machine Sections

-   -   FIG. 4A Front View     -   FIG. 4B Rear View

FIG. 5 Pre-Process Section

FIG. 6 Feed Hopper Operation

FIG. 7 Grinder/Dewaterer

FIG. 8 Process Section

FIG. 9 Process Drum

FIG. 9A Contaminant Door Detail

FIG. 10 Drum Drive

FIG. 11 Exit Baffle

FIG. 12 Post-Process Section

FIG. 13 Material Separator Assembly

FIG. 14 Pelletizer/Exit Conveyor

FIG. 15 VOC Filter/Dehumidifier

DETAILED DESCRIPTION OF INVENTION

The Invention uses a combination of mechanical disruption and thermal desiccation to remove water and break down the material. No chemical or biological agents are used in the process.

FIG. 1—External Shape and Size of the Invention.

The Invention is designed to occupy the same footprint as a standard green-waste dumpster such as used in a commercial kitchen and operate in the same manner, i.e. open it up and dump in the waste. The feed hopper is placed at an ergonomic 36″ from the floor to eliminate the need for lifting heavy waste containers above shoulder height.

FIG. 2—Process and Material Flow

The organic waste is placed into the isolating feed hopper (left side of diagram) that gravity feeds into the pre-processor. The pre-processor shreds the material using an industrial-grade grinder then removes ˜90% of the existing water with an auger press. The de-watered material is fed into the process drum to continue processing.

The process drum tumbles the material through hot air at the ˜90° C. process temperature. The material remains in the drum until it has dried and mechanically broken down sufficiently to be light enough to be entrained in the air stream exiting the drum. This separation technique is what allows new material to be added while the machine is in mid-process and is the primary patentable claim.

The air exits the process drum into the post-process section. Here, a separator removes the processed material from the airstream. The finished material falls to the bottom of the separator while the air is conducted out the top into the circulation blower. At the bottom of the separator is a pelletizing mechanism that compresses the finished material into a form that is both smaller and easier to handle, making it applicable for multiple biomass uses. An iris valve between the separator and pelletizer prevents the material from entering the pelletizer until a sufficient quantity has built up to make pelletizing efficient.

The air exiting the top of the separator is accelerated by the circulation blower into a dehumidifier that removes the evaporated water from the airstream. The dried air is ducted back to the process drum to be used again, conserving most of its original heat. The heater at the entrance to the process drum is needed only to replace the heat lost in process. The water condensed out of the air stream is routed back to the auger press in the pre-processor for removal by a common drain.

Another feature of the Invention is the ability to automatically separate inorganic contaminants from the finished product. Metal (e.g. from silverware) and glass that might be inadvertently placed into the feed hopper will be shredded and remains in the drum after all of the organics have been processed and removed. A sliding door is built into the drum that orients down when the drum is parked after a run. The door is cycled as the last step in a process cycle which dumps the contaminants into a bin for recycling or disposal.

FIG. 3—Internal Arrangement

The equipment in the machine is compact, yet easy access for maintenance has been retained. For efficiency, the flow paths are kept as straight and short as possible while maintaining a closed loop for energy conservation.

The base of the machine is a sturdy frame of 1½″ square steel tubing (1). This supports the Process Drum Assembly (2) from underneath, allowing access to the mechanisms from all sides once the Cabinet (3) is raised. The frame also directly supports the non-rotating Entry (4) and Exit (5) Endplates, the pre-process Grinder (6) and Feed Hopper Assembly (7). Within the lower part of the frame are the Dewaterer (8), Drum Drive Assembly (9), inorganic Contaminant Bin (10), Pelletizer (11) and Dehumidifier (12). The frame supports a Sub-frame (13) on the post-process side that locates the Material Separator Assembly (14) and the Exit Endplate (5). The sub-frame also supports the Exit Conveyor (17) and the VOC Filter Box (18).

The ductwork for the process air loop consists of a custom Square-Round Adapter (20) that joins the Circulation Blower (15) to the VOC Filter Box (18). Standard 8″ diameter HVAC ducting (25) completes the loop via the Dehumidifier (12) and airstream Heater Box (21).

The Machine Controller (19) is an industrial grade PC with sufficient I/O and processing capability to handle the required sensors and control algorithms. It is mounted, along with the sub-controllers for the Grinder, Drum Drive Motor, Dewaterer, Iris Valve, etc., in a NEMA class enclosure on the cabinet skin for efficient cooling.

FIG. 4—Machine Divisions

The processing equipment in the machine is divided into three sections: Pre-process, Process and Post-process as demarcated in the Figure.

Pre-Process Section

The parts of the Invention that make up the Pre-Process Section are shown in FIG. 5. It consists of the Heater Box (21), Feed Hopper Assembly (7), Grinder (6) and Dewaterer (8). The Pre-Process step is where the Invention achieves its large energy efficiency gains over extant prior art.

FIG. 5—Airstream Heater Box

The primary requirement for any desiccation process is a steady source of dry, heated air. In the Invention, this is provided by the Heater Box (21), which is mounted directly onto the Entry Endplate (4). Input to the box comes from the air return loop coming from the Dehumidifier (not shown in this view). The box is a generic volume large enough to accommodate electric, gas or steam heaters, giving users the option of whatever heat source best suits their needs.

FIG. 6—Feed Hopper Assembly (7)

The Isolating Feed Hopper allows new material to be introduced at any time while the Invention is operating without stopping the unit.

The Feed Hopper is comprised of a cylindrical Drum 20″ in diameter by 15″ wide (26) that rotates inside a fixed Housing (27) and is operated by means of a Handle (28). When in the “open” position (FIG. 6A) the opening in the drum is facing up, matching the opening in the fixed housing. In this position the waste (large arrow) can be added with the operator completely isolated from the grinder below. When the drum is rotated via the handle to the “closed” position (FIG. 6B), the hopper is closed off to outside access and the waste (double-ended arrow) is confined. Continuing to rotate the drum to the “dump” position (FIG. 6C) exposes the drum opening to the portion of the housing that forms a chute leading to the Grinder (6). The waste (large arrow) falls by gravity into the chute.

FIG. 7—Grinder/Dewaterer

Material dumped from the Isolating Feed Hopper (7) gravity-feeds into the Grinder (6). This is an industrial-grade grinder such as provided by JWC Environmental or Moyno, Inc. This class of grinder is capable of shredding any material that could be deliberately or inadvertently placed into the machine for processing. This includes metal (from silverware or beverage cans), glass, bones, shells, etc., that would jam regular food-waste processing devices. The cutting wheels on the grinder are specified to reduce the input material into particles no larger than 1×½cm (½×¼ inch). For safety, in addition to the mechanical isolation provided by the hopper, a Proximity Switch (29) on the housing prevents the Grinder from starting until the handle is fully down.

As the material falls from the grinder, it is conducted via a Bottom Hopper (30) into the Dewaterer (8). This is a commercial auger press such as provided by Kampwerth GmbH or JWC Environmental. This device consists of an Archimedes screw inside a tube and traces its basic design back more than 100 years as per the cited Patent #816,446. The convolutions on the screw start out wide apart at the base of the tube where the material enters, and get progressively closer towards the exit. This squeezing action removes up to 90% of the existing water which drains out of the bottom of the tube (36) and is then conducted out of the machine at the Drain Port (43, FIG. 1). The Dewaterer material Exit Port (37) feeds directly into the Process Drum Assembly (2) through an opening in the Entry Endplate (4).

Process Section

The parts of the Invention that make up the Process Section are shown in FIG. 8. It consists of the Process Drum Assembly (2), Drum Drive (9) and Contaminant Bin (10) including their sub-assemblies.

FIG. 9—Process Drum Assembly (2)

The Process Drum Assembly structure is a double-walled, stainless steel welded roll-up with Outer (39) and Inner (40) cylinders located by four Mixing Ribs (38) welded along their length. In addition to ensuring that the material being processed tumbles effectively through the hot air, these ribs center the Inner drum within the Outer one and stiffen the entire structure. This allows the large Contaminant Door (24) to be cut into the structure without weakening it.

In addition to strength, the Drum was designed with a double wall primarily to provide a cavity for the Contaminant Door operation so that no mechanisms protruded outside the drum where it might create a rotating hazard, or inside the drum where contamination with the waste material would greatly shorten the door mechanism's service life. As shown in the detail (FIG. 9A) the door seals against the Inner Cylinder (40) while its track runs on the inner surface of the Outer Cylinder (39). Another benefit of the dual-wall design is the ability to fill the remaining space with a foam-in-place insulation of very high “R value” which increases system efficiency.

The Drum is sealed at either end by a non-rotating Endplate. The Entry Endplate (4) forms the interface between the Pre-Process and Process sections. It has two holes, one of which allows entry of the hot air from the Heater Box (21) that is directly attached to the outer surface, and the other is for the introduction of the ground and de-watered waste material from the exit port of the Dewaterer (8). The Exit Endplate (5) is the interface between the Process and Post-Process sections and has the Exit Baffle (22) attached directly to its inner surface (the function of the Exit Baffle is covered separately below). Both Endplates are structurally independent from the Drum and are sealed against the rotating Drum by an industrial felt seal.

FIG. 10—Drum Drive (9)

The Drum rolls on four Wheels (31), the front two of which are driven and the back two are idlers. The Drum is rotated by the Drum Drive consisting of a 5 HP electric motor (32) and a Chain Drive Transmission (33) that transfers motor torque to the two driven Wheels. The ratios of the sprockets in the transmission are chosen such that the Drum rotates with 0.8 g of radial acceleration at its inner surface. This level of acceleration will keep the material attached to the inner wall by centrifugal force up to an angle of approximately 55° from the horizontal at which point it detaches and falls through the hot air stream. The hot air inlet in the Entry Endplate is strategically located along the ballistic path that the material will take as it falls from the drum.

The tumbling action not only keeps the material mixed and continuously passing through the desiccating air stream, but it also causes the mechanical breakdown of the material due to repeated impacts with the Drum inner surface and the harder material. This progressively increases the surface area of the material which speeds up processing. The material continues to be processed in the drum until it is light enough to be entrained in the airstream through the Exit Baffle (22).

Materials that do not break down at this temperature, e.g. bone, glass and metal contaminants, remain in the drum after all organic material is processed and a Contaminant Door (24) opens to dump them into the Contaminant Bin (10) for recycling or disposal.

FIG. 11—Exit Baffle (22)

The key to the continuous-processing aspect of the Invention, and the primary patentable feature, is the ability to separate out the finished desiccated material from that still being processed. This is done using a tortuous-path Baffle (22) attached to the inner surface of the Exit Endplate (5). The Baffle employs an optically-dense series of plates (23) arranged at progressively decreasing angles and lengths as the path progresses upward. The optically-dense nature of the baffle prevents any heavy materials that may ricochet off of the Drum inner surface into the Baffle housing from traveling past the second plate.

The material, indicated by the wide arrows, enters the Baffle at the bottom. The entire bottom of the unit is open to keep the initial airflow slow but the geometry of the path around the first baffle plate (23) accelerates it for a relatively high airflow that gets progressively slower again as the path moves upward. This ensures that the finished light material will be drawn in, but the momentum reversals caused by the plates (curved arrows), ensures that only the material truly entrained in the airstream will successfully negotiate the path. The slowing airflow towards the top prevents all but the very lightest (i.e. completely desiccated) material from reaching the Exit Port (34). Material light enough to be entrained, but still too heavy to make it to the exit will oscillate up and down in the hot air stream until it dries out enough to exit.

Post-Process Section

The parts that make up the Post-Process Section are shown in FIG. 12. It consists of the Material Separator Assembly (14), Pelletizer (11), Exit Conveyor (17), Square-Round Adapter (20), VOC Filter Box (18), Dehumidifier (12) and the Ductwork (25) completing the loop back to the Heater Box (not shown). Most of these components are supported or located by the Sub-frame (13).

FIG. 13—Material Separator Assembly (14)

Air with the entrained material leaving the Exit Baffle (22) goes directly into the Material Separator Assembly (14) by means of a transfer duct passing through a hole in the Exit Endplate (5). This assembly's purpose is to remove the processed material from the airstream and it consists of a Cyclone Separator (35), the Circulation Blower (15) and an Iris Valve (16). The transfer duct passing through the Exit Endplate is part of the Cyclone Separator.

Cyclone Separators, which have no moving parts outside of the air itself, are used extensively in industry to remove solid material entrained in airstreams. They consist of a hollow chamber shaped like a cylinder stacked on top of a funnel. The air with the entrained material (segmented arrows) enters on one edge of the cylindrical part of the chamber. Momentum of the material keeps it moving along the outer edge of the chamber, held by centrifugal force (wide curved arrows). The exit for the air (narrow curved arrows) is in the center of the top of the chamber where the Circulation Blower (15) is attached. Since the volume of the chamber is large compared to the duct that brought the air and material in, the velocity of the air moving inside the Separator is much slower. Too slow, in fact, to keep the processed material entrained in the stream and it falls to the bottom while the air exits through the Blower.

The separated material accumulates on top of an Iris Valve (16) at the bottom of the “funnel” section until enough material has been produced to be efficiently pelletized. This is a commercial component such as the Mucon series of valves provided by Kemutec.

FIG. 14—Pelletizer/Exit Conveyor

Once sensors detect that a sufficient quantity of material has accumulated on top of the Iris Valve (16), it can be pelletized using a commercial unit such as provided by Buskirk Engineering or Kahl GmbH. The Pelletizer (11) is started and the Valve (16) opened. The Circulation Blower (15) is simultaneously shut off to prevent air from backstreaming through the Pelletizer. After the Pelletizer is finished forming the material into reusable pellets, the Iris Valve is closed, the Pelletizer is shut off and the Circulation Blower re-started. The Exit Conveyor (17) carries the finished pellets up to the machine exit at a height that allows them to fall into a standard 32 gallon receptacle. The Exit Conveyor is a small ladder or auger unit usually supplied by the manufacturer of the pelletizer and designed specifically to work in concert with it. The other function of the conveyor is to give the pellets time to cool from their 200° F. forming temperature to one low enough to be safe for immediate handling and non-damaging for plastic receptacles

FIG. 15—VOC Filter/Dehumidifier

After the solid material has been separated from the airstream there are two gaseous components to be dealt with. First, any volatile organic compounds (VOC's) that may have been generated by the process heat must be removed (Federal regulations limit the release of VOC's into the atmosphere). Second, the water removed from the material by phase-change in the process drum, must be condensed out of the stream before the air is re-heated and send through the Drum again.

The first of these is removed by an activated carbon filter housed in the VOC Filter Box (18) which is connected to the Material Separator Assembly (14) by means of the Square-Round Adapter (20). The VOC Filter Element (41) is placed diagonally across the housing thus forming two plenums, one on either side for the inlet and outlet. This lowers the airflow speed through the filter reducing the pressure drop. The filter slot is located behind a matching door in the cabinet (44, FIG. 1) for ease of replacement and is placed at an ergonomic height for that task.

The water vapor in the stream is removed by an industrial Dehumidifier (12). This unit is similar to a standard phase-change air conditioner in that it chills the air stream below the dew point causing the water to condense out. Unlike an air conditioner, however, the refrigerant condenser is placed in the airstream at the exit of the unit to add back the heat initially removed so that there is no net loss of heat. Additionally, there is a linear blower at the exit to reverse the pressure drop of passing through the two heat exchangers. The water condensed out by the unit exits from its drain (42) which is conducted to the Dewaterer (8) where it joins the water from that component's drain (36) which collectively exit out the system drain (43). 

1. Greater efficiency Over composting On-site processing, no transporting of waste with attendant petroleum use and emissions Over extant desiccators Process air recycled: No vent to the outside, no heat wasted Process independent of heat source: Electric, natural gas and steam heated versions are equally plausible and accommodated in the design Pre-processor reduces particle size and removes up to 90% of the water prior to desiccation, reducing desiccation time (thus energy use) by more than half Requires no process water (unlike traditional pulpers and grinder/compactors)
 2. Higher Speed: Process Time 10 to 15 hours (new material can be added at any time) Over composting Process Time: 90 days, must be turned every week. Over extant desiccators Process Time: 18 to 24 hours (machine locks during processing, new material must wait for cycle to finish)
 3. No greenhouse gas generated Over composting CO₂ generated Over landfill
 4. Ease of Use: Any invention must be easy and intuitive to use if it is to be accepted and used. This Invention has deliberate design features to make it as “user friendly” as possible in commercial kitchens where many of the staff who will be using it are not technically sophisticated. Specifically: Continuous process (not batch processor): Can be used exactly like a dumpster: open the lid (hopper), dump in waste, close lid (hopper). No machine operation to think about. Accepts all compostable waste (including paper waste and “compostable” plastics): No pre-sorting required Tolerates non-compostable material: silverware, glassware, plastic film, etc. that unavoidably get tossed out with the waste. These will not jam machine and are automatically sorted out Feed Hopper Capacity: 1 cu. ft. (˜7 gallons): many kitchens use 5 gallon buckets for waste disposal since that's close to the OHSA 40 lb carry limit (5 gallons of high-water-content waste weighs ˜35 lbs). The hopper is sized to accept a full 5 gallon bucket with some margin Feed Hopper Height: Ergonomically placed at 36″ from the floor to avoid stress injuries from the high-lifts associated with standard dumpsters
 5. Easily adapted to greater automation: For users with waste receptacles larger than a 5-gallon bucket, the Feed Hopper (7) can be replaced with an interface for a commercial dump lift that can accommodate up to a standard 32 gallon receptacle. Since the unit can accept waste continuously and randomly, it can be interfaced to a “scraping station” in a commercial kitchen with a short external conveyor. 